There exists an everlasting problem within pharmacy to be able to administer a therapeutically active compound as close as possible to the colon or preferably in the colon, in order to thereby to eliminate the risk of adverse influence on the active compound by the gastric juice, or to prevent irritation of the ventricular mucous membranes, or to obtain a therapeutically effect in the lower part of the gastrointestinal tract. A further problem is to obtain a steady, preferably linear release of a therapeutically active compound in order to give an steady blood plasma level of the therapeutically active compound, without an initial release peak, which may cause side-effects due to too high concentrations in the body of the therapeutically active compound.
In EP-A-No. 0 040 590 there is disclosed an oral pharmaceutical composition comprising a core containing a therapeutically active compound, which core has been coated with a layer comprising 10 to 85% by weight of an anionic polymer soluble at a pH above 5.5 and 15 to 90% by weight of a water insoluble polymer selected from quaternary ammonium substituted acrylic polymers. Such a product gives, however, too high a permeability in gastric juice and is only suitable for therapeutically active compounds having a relatively low solubility in all acidic environment viz. a solubility of &lt;1 g/100 mi.
There is no real method or composition known today within pharmacy which can protect compounds which are very soluble in acidic environment and provide them with an adequate release profile in the more neutral pH of the small intestine and the large intestine after an attack by gastric acid during passage through the ventricle.